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[KC8NXB]

Does anyone know if there is a dual band antenna that will pick up repeaters in a 50-mile radius? I can put it up about 16 to 18 feet.

[WB6BYU]

What is your terrain like?  That makes a huge difference
in your coverage distances.

Is the 16-18' to the base of the antenna, or to the top?
If it is to the base, is there a limit on how tall the antenna
can be?  Or how large in diameter?

Are you willing to consider a beam antenna that you can
rotate to the desired direction for each repeater?


All of these make a difference.

I've hit repeaters 100 miles away with my HT.  On low power.
In other cases, I can't hit a repeater 10 miles away, if it is
behind a hill.

Nobody can give you a practical answer (other than "try it
and see") without knowing more about your situation.


Edited to add:

Let me add a bit more information.  For an omnidirectional
antenna, gain is a function of antenna length.   The longer
(taller) the antenna, the higher gain.  A 2m antenna about
20' long has roughly 6 dB gain over a dipole that is 3' long.
You simply can't get more gain with a shorter length, but
a poorly-designed antenna can be lower.  Taller antennas,
often implemented by a stack of vertical dipoles spaced
along the edge of a tower, can have even higher gain -
that's why I asked if there was a maximum height to the
antenna (otherwise, we could suggest a 200' tall antenna,
even if the base were mounted 10' off the ground).

And height above ground at the top of the antenna can be
a reasonable indicator of performance.  If your top height
is limited to, say, 20', then there isn't a significant practical
difference between a 3' antenna on a 17' mast and a 20'
antenna sitting on the ground.  In fact, the simple dipole or
ground plane may well work better than the antenna with
a higher nominal gain, because the average height above
ground is higher.

So you can do a quick comparison among VHF/UHF antennas
simply by comparing the lengths.  Two omnidirectional antennas
about the same length will have about the same gain in the
real world, regardless of what numbers the Marketing department
may have pulled from invented.

In flat, open terrain, height to the top of the antenna typically
makes the most difference.  In hilly terrain, the relative heights
of the transmitter and receiver compared to the hills between
them becomes more critical.  If the repeater is several thousand
feet up on a hill, it will be much easier to reach, and simple
antennas may be adequate, especially if your location has some
height as well.

A beam antenna can have much higher gain than a practical
omnidirectional antenna, but you have to point it in the right
direction to make use of it.  So, if you need more gain with a
limited maximum height, that might be another approach.

[KC8NXB]

Thank you for your helpful information. The base is 16' to 18' above ground. Can't go any higher until next summer. I am in a flat area, nothing around me but 1 story brick homes. Can't due a beam. I have a Comet GP-3 at present. Looking for a better antenna. Looking to spend under $250. Had to get out of HF radio due to a hearing problem. I can hear UHF and VHF much better especially digital.

[K5LXP]

Separate from the antenna gain discussion is radio horizon, line of sight.  If the station you're trying to work is beyond line of sight, then no amount of antenna gain will make a difference.  Conversely, if the station is within line of sight then gain isn't as critical except right on the very fringe of coverage.  So height is going to be the major contributor to range, gain will help with signal strength.  Point of all this is if you're not hitting the station you want with your GP3 then likely going to a higher gain or different antenna probably won't help. 

Mark K5LXP
Albuquerque, NM

[KC8NXB]

Thanks Mark. As they say, "height is mite".

[K4GTE]

I hit repeaters in my area 100 miles away, sometimes farther depending on propagation. I use a Diamond X510 mounted on a 30 foot mast, overall height is about 50 feet. Transceivers are an Icom IC 9700 and a Yaesu FT 2980. 100 watts, and 80 watts.

[K5LXP]

This doesn't factor terrain but gives an idea what one might expect for line of sight range:

http://www.calculatoredge.com/electronics/lineofsight.htm

One can put in your station height and say the height of a distant repeater to see what the limits are.  As an example, with a repeater at 5000ft HAAT the range is 100 miles, not unusual for repeaters around here.

Mark K5LXP
Albuquerque, NM

[RR999]

On the topic of dBs, aside from antenna gain, what is the type and distance of the coax? At VHF and especially UHF, feedline losses can add up fast.

[KC8NXB]

Thanks everyone. I use 75' of RG8.

[KD6VXI]

RG8 is meaningless, other than to specify the physical size of the cable now.  The military dropped RG numbers decades ago.

Every military installation I put in used Times Microwave LMR400 or better. Not ultraflex, not an off brand.  Times Microwave.  The stopped allowing Belden 9913 when it started being a water hose.

I would check to see if the coax is worth a damn before

Even 9913, at 440 and 75 feet has just over 2dB of loss.  At 2 meters it's 1.15.  And this is assuming a flat match.  Swr loss is real, and Wil cut into your ERP and received signal even more.

For instance at 1.5 swr, 75 feet of 9913 with a 1.5 swr will lose 25 percent of your power.

Granted you will only see this make a difference in seriously small signal comms.....  But add a bunch more loss if using some off brand coax marked as RG8.... And it will start making a big difference.

--Shane
WP2ASS / ex KD6VXI

[W9IQ]

Keep in mind that during receive, there is typically very little additional loss due to SWR as the line is essentially matched. Any additional losses during receive will be primarily due to antenna re-radiation.

- Glenn W9IQ

[W9IQ]

There are some tools that can help to estimate coverage. But since you have an existing station, it is good to compare the results of these tools to your current experiences. Here is 2 meter a coverage map of from your QTH at an elevation of 18 feet with a 3 dBi antenna talking to a repeater with an antenna 100 feet in the air. Does this look close to your current experience?



- Glenn W9IQ

[KC8NXB]

Thanks, Glen, for the map. It shows about a 15 mile radius. I can pick up repeaters out to 20 or 25 miles, they must be higher up. The coax is RG8U from Alpha in Florida, made in USA.

[AI5BC]

The coax is RG8U from Alpha in Florida, made in USA.

Sounds like no-name generic coax. There is RG8 coax and then there is RG8 coax. For example, a generic ham coax 100 feet insertion loss is 2.8 dB @ 144 MHz and 5.1 dB @ 450 MHz. Whereas something like LMR400 is 1.5 dB @ 144 MHz and 2.7 dB @ 450 MHz. You get what you paid for.

[WA3SKN]

A 50 mile radius might be a stretch for FM.  You might want to start thinking about a beam antenna for that range.  Do you need to rotate it?  It makes a cost difference.
Or think SSB.  6m, 2m, 70cm on sideband could make that range.

-Mike.